Effects Of Long-Term Plastic Film Mulching And Straw Incorporation On Soil Organic Carbon Turnover

Soil organic carbon plays an important role in maintaining soil structure and fertility,controlling“Greenhouse Effect”and so on.It is necessary to maintain or improve soil organic carbon effectively for sustainable development of agriculture and alleviating global warming.Plastic film mulching has been widely used in semi-arid regions of the Loess Plateau because of its characteristics of increasing temperature,preserving water and increasing yield.The increase in soil temperature and moisture by use of plastic film mulching have enhanced the mineralization of soil organic carbon,simultaneously promoted the growth of crop root system to increase organic carbon input.Therefore,soil organic carbon achieved the dynamic balance of carbon input and output.Straw could increase the content of soil organic carbon as a renewable biological resource applied to farmland.It is a good measure to improve soil fertility and physical structure.However,there are few studies on the effects of plastic film mulching and straw return on the turnover rate and stability of different organic carbon pools in soil.In 2009,the field experiment was carried out at Xiaokangying Township Test Station in Yuzhong County,and four treatments were set up under the mode of ridge and furrow sowing:?1?no mulching and no straw incorporation?Control?;?2?straw incorporation without mulching?S?;?3?mulching without straw incorporation?M?;?4?mulching and straw incorporation?S+M?.The four treatments were repeated three times and the blocks were randomly arranged.Soil samples were collected during maize harvest in 2017,using ¹³C isotope tracer?natural abundance?and soil relative density grouping techniques to analyze:?1?changes of soil organic carbon contents and different soil carbon pool contents in 0-15,15-30,30-45 cm soil layers;?2?the effects of mulching and straw incorporation on the source and turnover rate of soil organic carbon and its components in different soil layers;?3?the stability of 0-15 cm soil heavy fraction organic carbon by cultivation experiment.The main results are as follows:1.Film mulching had no significant effect on the total organic carbon?SOC?of 0-45 cm soil,straw incorporation increased 0-30 cm SOC significantly,but had less effect on 30-45 cm SOC,of which,0-15 cm SOC increased by 2.6-3.7%and 15-30 cm SOC increased by 1.8-2.3%under straw incorporation.Plastic film mulching reduced 0-30 cm soil light fraction organic carbon?LFOC?,whereas straw incorporation significantly increased 0-30 cm LFOC,both had less effect on 30-45 cm LFOC,among them,compared with no mulching,plastic film mulching reduced0-15 cm LFOC 24.2-26.3%and reduced 15-30 cm LFOC 14.0-15.1%;straw incorporation increased 0-15 cm LFOC 59-63.6%and 15-30 cm LFOC 50%-55.14%compared with no straw incorporation.Plastic film mulching increased 15-30 cm soil heavy fraction organic carbon?HFOC?2.3-5.5%;0-15 cm HFOC increased by 11.7-24.4%and 15-30 cm HFOC increased by11.4-15.0%under straw incorporation.2.Film mulching had no significant effect on the proportion of maize derived LFOC,while straw incorporation significantly increased the proportion of maize derived LFOC,of which 0-15cm increased 67.7-83.3%,15-30 cm increases by 47.7-64.7%and 30-45 cm increased by13.8-55.2%.Both of plastic film mulching and straw incorporation significantly increased the proportion of 0-30 cm maize derived HFOC.In the 0-15 cm soil layer,plastic film mulching increased by 37.7-40.0%,and straw incorporation increased by 156.2-160.7%;In the 15-30 cm soil layer,plastic film mulching increased by 65.1-81.1%,and straw incorporation increased by145.8-169.6%.In the 30-45 cm soil layer,film mulching reduced the proportion of maize derived HFOC 46.3-48.4%,whereas straw incorporation increased by 47.1-53.0%.3.Film mulching significantly reduced the cumulative mineralization of 0-15 cm HFOC by2.40-10.7%during 90 days incubation,while straw incorporation increased by 6.64-16.5%.Both plastic film mulching and straw incorporation significantly reduced C4-C mineralization of 0-15cm HFOC,plastic film mulching reduced by 11.5-26.8%compared with no mulching,and straw incorporation reduced by 43.0-52.9%compared with no straw incorporation.The results indicated that plastic film mulching could maintain soil organic carbon content and accelerate the turnover of HFOC in plough layer,and straw incorporation could effectively increase soil organic carbon content,accelerate the turnover of 0-45 cm light and heavy fraction organic carbon.At the same time,film mulching and straw incorporation both increased the stability of new carbon in the heavy fraction of topsoil.